JP-A-2004-114343 discloses a technology for forming concentration patches (dither patterns) by changing concentration patch data (dither pattern data) for each printing condition and using results of measuring of concentrations of the concentration patches to perform concentration correction (gamma correction) on print images.
Developing-bias correction is sometimes performed before gamma correction is performed. However, if the developing-bias correction is performed with concentration patches (images for correction) formed by LED exposure with a large amount of defocusing, there is a fear that correction widths of developing biases will become larger than expected and the reproducibility of isolated dots, thin lines, and the like will become lower.